Transfer printing apparatus of electrophotographic apparatus

ABSTRACT

In transfer printing apparatus of electrophotographic apparatus of the type wherein a receptor sheet is urged against a photosensitive element carried by a rotary drum by means of a transfer printing roller so as to transfer print an electrostatic latent image formed on the photosensitive element onto the receptor sheet there is provided a stationary separating member between the receptor sheet and the photosensitive element. Preferably, the separating member comprises a pair of strips which are disposed at an angle with respect to the direction of movement of the receptor sheet.

United States Patent [191 Suzuki et al.

[ July 16, 1974 TRANSFER PRINTING APPARATUS OF ELECTROPHOTOGRAPHICAPPARATUS [75] Inventors: Ryuzo Suzuki, Tokyo-to; Seiichi Miyakawa,Nagareyama; Masanori Watanabe, Tokyo-to, all of Japan [73] Assignee:Katsuragawa Denki Kabushiki Kaisha, Tokyo-to, Japan [22] Filed: July 20,1972 [21] Appl. N0.: 273,425

[30] Foreign Application Priority Data July 28, 1971 Japan 46-57078 July28, 1971 Japan 46-57079 [52] US. Cl 355/3, 355/64, 355/110 [51] Int.Cl.. G03g 15/00, G03b 27/10, G03b 27/32 [58] Field of Search 355/3, 64,110

[56] References Cited UNITED STATES PATENTS 1,900,878 3/1933 Hopkins355/64 Salger 355/110 Hyosaka lto 355/3 Primary ExaminerJ0hn M. HoranAttorney, Agent, or FirmBosworth, Sessions &

McCoy [5 7] ABSTRACT In transfer printing apparatus ofelectrophotographic apparatus of the type wherein a receptor sheet isurged against a photosensitive element carried by a rotary drum by meansof a transfer printing roller so as to transfer print an electrostaticlatent image formed on the photosensitive element onto the receptorsheet there is provided a stationary separating member between thereceptor sheet and the photosensitive element. Preferably, theseparating member comprises a pair of strips which are disposed at anangle with respect to the direction of movement of the receptor sheet.

2 Claims, 6 Drawing Figures TRANSFER PRINTING APPARATUS OFELECTROPHOTOGRAPHIC APPARATUS BACKGROUND OF THE INVENTION This inventionrelates to apparatus for separating a receptor sheet or a transferprinting paper from a photosensitive drum of an electrophotographicapparatus after an electrostatic latent image formed on the surface ofthe drum has been transfer printed onto the receptor sheet.

In one type of electrophotographic apparatus, an electrostatic latentimage formed on the surface of a rotary photosensitive elementcorresponding to an original is transfer printed onto a receptor sheetby means of a transfer printing roller which acts to urge the receptorsheet against the photosensitive element and then the transfer printedlatent image is developed to obtain a visible image. However, it isdifficult to separate or peel off the receptor sheet from thephotosensitive element because the electrostatic force of the latentimage attracts the receptor sheet toward the photosensitive element.

To positively separate the receptor sheet from the photosensitiveelement it has been proposed various devices including (1) a devicewherein a peel off member is contacted against the periphery of therotary photosensitive element for mechanically separating the receptorsheet, (2) a device wherein the leading edge of the receptor sheet isslightly curved away from the periphery of the photosensitive elementand a peel off member is disposed with its inner end slightly spacedapart from the periphery of the rotary photosensitive element so as notto damage it, (3) a device wherein after the transfer printing an airjet is applied to the leading edge of the receptor sheet to separate itfrom the photosensitive element, (4) a device wherein a suction drum isarranged behind the receptor sheet to separate it by suction (5) andcombinations of these devices. However, with devices (1) and (2) it isimpossible to transfer print the latent image along the entire length ofthe receptor sheet thus decreasing the effective area thereof. Devices(3) and (4) not only require the provision of a source of pressurizedair but also are difficult to positively peel off the receptor sheetwhere the quantity of the charge of the latent image is large as in thecase of a perfectly black picture.

SUMMARY OF THE INVENTION Accordingly, it is an object of this inventionto provide a new and improved apparatus for separating a receptor sheetfrom a photosensitive element.

Another object of this invention is to provide novel separatingapparatus of simple construction which can efficiently separate areceptor sheet from a rotary photosensitive element after theelectrostatic latent image has been transfer printed but does notinterfere with the transfer printing.

According to this invention there is provided transfer printingapparatus of electrophotographic apparatus of the type wherein areceptor sheet is urged against a photosensitive element carried by arotary drum by means of a transfer printing roller so as to transferprint an electrostatic latent image formed on the photosensitive elementonto the receptor sheet, characterized in that a stationary supportingmember is interposed between the receptor sheet and the photosensitiveelement.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 shows a side view, partly broken away, of a photosensitive drumprovided with separating apparatus embodying the invention;

FIG. 2 is a plan view of a transfer printing roller and separatingmembers;

FIG. 3 shows a side view similar to FIG. 1 but showing a modifiedembodiment using two transfer printing rollers;

FIG. 4 is a plan view showing the transfer printing roller andseparating members of the embodiment shown in FIG. 3;

FIG. 5 is a plan view similar to FIG. 4 showing modified transferprinting rollers and FIG. 6 is a plan view showing a modified separatingmember and modified transfer printing rollers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, arotary photosensitive drum l0 utilized for forming an electrostaticlatent image on the periphery thereof may be any suitable constructionand the latent image may be formed by any suitable method. In theillustrated example, the drum 10 carries a cylindrical photosensitiveelement 11 including an electrode layer 14, a photoconductive layer 13and a transparent highly insulative layer 12 which are bonded togetherinto an integral cylindrical structure. Where the drum 10 is made ofmetal, the electrode layer 14 may be omitted. The photoconductive layer13 may be made of any photoconductive material or phosphor manifestingpersistent internal polarization, such as CdS, Zn CdS, CdS or Zn CdSactivated with copper or silver, selemium, anthraceneor TeSe. A latentimage may be formed on the surface of the highly insulative layer 12 byapplying a first electric field across the photosensitive element todeposit a charge of one polarity on the surface of the highly insulativelayer thereby establishing substantially uniform persistent internalpolarization in the photoconductive layer, applying a second electricfield across the photosensitive element to deposit a charge of theopposite polarity on the surface of the highly insulative layer, andprojecting a light image upon the photoconductive layer through thehighly insulative layer concurrently with the application of the secondelectric field thereby forming the latent image on the surface of thehighly insulative layer. Above described method is advantageous in thatthe latent image is not erased by later irradiation of light so that itis possible to carry out the transfer printing and developing operationsin the bright. Where the photoconductive layer contains a large numberof deep charge trap levels, as in the case of Zn CdS activated withsilver or copper, it is desirable to irradiate the latent image withuniform light from an electric lamp for example.

In the case of the conventional xerography, the latent image is formedby applying an electric field across the photosensitive element in thedark and then projecting a light image. In this case, however, as thelatent image is readily erased by light it is necessary to carry out thetransfer printing and developing operations in the dark as is well knownin the art.

To transfer print the latentimage thus formed on the periphery of thephotosensitive element onto a receptor sheet P, usually an ordinarypaper, there is provided a transfer printing roller 15 which is made ofrubber, for example, and is urged against the periphery of the rotaryphotosensitive element 11 by suitable means, not shown. According tothis invention, one, two or more spaced apart seperating members 16 of afiber, string or tape of a synthetic resin such as nylon andpolytetrafluoroethylene or metal foil are provided between stationarymembers 17, to extend through the nip between photosensitive element 11and transfer printing roller 15 and the receptor sheet P is fed betweenthe separating members and the transfer printing roller. Among variousmaterials, strips of polytetrafiuoroethylene are found to be mostsuitable because they have flat and smooth surface so that they do notdamage the photosensitive element and receptor sheet by the contactfriction, and because they have small elongation, a large shear strengthand a long life. Even when a conductive material such as a metal foil orsheet is used, the electrostatic latent image would not be erased solong as the contact pressure between the separating members and the.photosensitive element is low. Conductive material has a largedurability. As shown in FIG. 2, the separating members are disposed atan angle with respect to the direction of movement of the receptor sheetP which is indicated by arrow A. Since the separating members aredisposed between the rotary drum andthe receptor sheet they act toseparate the receptor sheet from the rotary drum after transferprinting. As the rotary drum is rotated, the separating membersarecontacted by the surface of the photosensitive element so that onemay consider that the latent image would be erased or certain portion ofthe latent image would not be transfer printed. Actually, however, itwas found that the latent image can be satisfactorily transfer printedwhere a relation a/W sin 0 is satisfied, where W represents the contactwidth between the peripheries of the photosensitive element and transferprinting roller and a the width of a separating member. Moreover, sincethe separating members are disposed at an angle with respect to thedirection of movement of the receptor sheet P it is possible to preventthe receptor sheet from crimpling. While separating members of anynumber may be used, the material from which the separating members areformed should be wear resistant and should not damage the surfaces ofthe photosensitive element and the receptor sheet. The result ofexperiment shows that a nylon fiber having a diameter of 0.2 mm and atape of polytetrafluoroethylene having a thickness of 0.05 mm and awidth of 3 mm are satisfactory. The separation of the receptor sheet canbe enhanced where the receptor sheet P is fed into the nip and removedfrom the nip, both at an angle with respect to the separating members,as diagrammatically shown in FIG. 1. Further, the separating members maybe inclined in the same direction, but better results are obtained whenthey are inclined in the opposite directions as shown in FIG. 2.

In the modified embodiment shown in FIGS. 3 and 4, two parallel transferprinting rollers a and 15b which are spaced apart in the direction ofmovement A of the receptor sheet are provided to increase the effectivearea of the contact width W. With this arrangement, there is no fear ofmis-transfer printing even when the width a of the separating members 16is large. More particularly, as shown in FIG. 4, when the latent imageis transfer printed by transfer printing roller 15b, the

portions of the latent image corresponding to widths 0 may not beeffectively transfer printed by the interference of the separatingmembers 16. However, these portions are. not interferred by theseparating members 16 while the latent image is transfer printed by theother transfer printing roller 15a.

In another embodiment shown in FIG. 5, the transfer printing rollers 15aand 15b are provided with reduced diameter portions 18 whichreceiveseparating members 16 so as not urge them against the peripheryof the photosensitive element.

In the modification shown in FIG. 6, the separating member 19 takestheform of a web of a synthetic resin. In this case, transfer printingroller 15b is formed with a reduced diameter portion 18 at the middlesection thereof, whereas the other transfer printing roller 15a isprovided with reduced diamter portions 18 on the opposite end sections.The separating member 19 is provided with windows 20b and 20a at thelarger diameter protions of the transfer printing rollers 15b and 15a,respectively. Windows 20a and 20b are staggered in the lateral directionwith respect to the direction of movement of the receptor sheet. Thus,the entire width of the receptor sheet interposed between the transferprinting rollers and the separating member is urged against theperiphery of the photosensitive element to effect efficient transferprinting of the latent image.

According to the embodiments shown in FIGS. 5 and 6, since theseparating member is not urged against the periphery of thephotosensitive element by the provision of reduced diameter portionsl8'there is no fear of damaging by friction the surface of thephotosensitive element and the latent image which has been transferprinted on the surface of the receptor sheet.

While the invention has been shownand described in connection with aparticular method of forming an electrostatic latent image, it will beclear that the latent image can be formed by any method and by utilizingany one of many known photosensitive elements. If desired, suitablevoltage may be applied between the rotary drum and the transfer rollerto enhance transfer printing.

We claim:

1. In apparatus for transfer printing of electrophotographic imagescomprising a rotary drum provided with a photosensitive element on whichan electrostatic image is to be formed, a receptor sheet and a transferprinting roller for urging said receptor sheet against the surface ofsaid photosensitive element to transfer print said latent image ontosaid receptor sheet, the improvement which comprises a stationaryseparating member made of a sheet material having a width at least equalto the width of said receptor sheet interposed between said receptorsheet and said photosensitive element, said transfer printing rollerbeing formed with a large diameter section and said separating memberbeing provided with a window to receive said large diameter section. v

2. The transfer printing apparatus according to claim 1 wherein thereare provided a plurality of parallel transfer printing rollers which arespaced apart in the direction of movement of said receptor sheet and areprovided with a large diameter portion and a reduced diameter portion,the large diameter portions of adjacent transfer rollers being staggeredwith respect to the direction of movement of said receptor sheet.

1. In apparatus for transfer printing of electrophotographic imagescomprising a rotary drum provided with a photosensitive element on whichan electrostatic image is to be formed, a receptor sheet and a transferprinting roller for urging said receptor sheet against the surface ofsaid photosensitive element to transfer print said latent image ontosaid receptor sheet, the improvement which comprises a stationaryseparating member made of a sheet material having a width at least equalto the width of said receptor sheet interposed between said receptorsheet and said photosensitive element, said transfer printing rollerbeing formed with a large diameter section and said separating memberbeing provided with a window to receive said large diameter section. 2.The transfer printing apparatus according to claim 1 wherein there areprovided a plurality of parallel transfer printing rollers which arespaced apart in the direction of movement of said receptor sheet and areprovided with a large diameter portion and a reduced diameter portion,the large diameter portions of adjacent transfer rollers being staggeredwith respect to the direction of movement of said receptor sheet.